Pulmonary transvascular fluid dynamics in sheep during hemorrhage.

The effects of hemorrhage on pulmonary hemodynamics and lung transvascular fluid dynamics were studied in sheep. We found that 2 hr of hemorrhage caused a fall in lung lymph flow (p less than 0.05) and no significant change in lymph protein concentration. The fall in lymph flow was not due to decreased vascular surface area since the regional distribution of pulmonary perfusion was not altered during hemorrhage; however, the decrease in lymph flow was associated with decrease (p less than 0.05) in the calculated pulmonary microvascular pressure. The extravascular lung water lung content per g bloodless dry lung was increased (p less than 0.05) in the hemorrhaged sheep from the control values. Pulmonary edema was not due to increased lung vascular endothelial permeability since the net transvascular protein flux was not increased. The finding that pulmonary edema occurred despite the consistent decreases in lymph flow suggests that edema may be due to hemorrhage-induced lymphatic "failure" or that edema fluid is sequestered in spaces (e.g., endothelial cells) where if cannot be drained by the lymphatics.